1. Field of the Invention
The present invention relates generally to liquid crystal shutters and more particularly to a method for fabricating liquid crystal shutter displays using a single mode visible laser.
2. Brief Description of Related Art
The fabrication of liquid crystal shutter display devices requires the delineation of multiple parallel horizontal segments of indium tin oxide, separated by narrow spaces, on the surface of a sheet glass substrate. The narrow spaces are typically in the order of 4-10 microns wide and provide electrical isolation of the stripes to facilitate synchronization of the switching of the liquid crystal with the vertical raster of a CRT.
Typical contemporary production techniques in the liquid crystal display industry employ positive working photoresists for reproducing the image of a photomask on the surface of the glass substrate. Briefly, to produce the above-described parallel segments, a glass substrate having a thin indium tin oxide conductive layer on its surface is coated with photoresist. A photomask with the appropriate segment-spacing pattern is brought within close proximity to the photoresist coating and a UV lamp behind the photomask is illuminated. The light striking the photoresist causes a photochemical reaction that allows a developing solution to remove photoresist from all areas exposed to the UV light.
The achievable space dimensions between the segments, and their tolerances within the photoresist, are determined by the optical system used in the fabrication, including: the dimensions on the photomask; the spacing between the mask and substrate; and, the wavelength of the UV lamp. Current high volume exposure tools in the liquid crystal display industry are capable of resolving lines on the order of .gtoreq.20.mu. at their best performance. Typical contemporary proximity aligners could be set up for small exposure gaps on the order of sub 10.mu., but this would cause undo pick-up of photoresist particles off of the surface of the substrate and result in repeating defects unless the photomask was frequently cleaned.
An alternative exposure tool for producing the requisite spaces between the parallel segments is a step and repeat aligner. In a step and repeat aligner, a photomask is placed at a predetermined distance from the substrate and an optical system reduces the image of the photomask by some integer number (typically 2x to 5x) onto the surface of the substrate. The substrate is then moved by a stage and the exposure is repeated. In this fashion, exposure is achieved by stepping the substrate and repeating exposure, making sure that, each time, the mask is aligned properly to either the previously exposed layer, or to the adjacent layer. While such tools are capable of resolving the narrow lines needed for defining the horizontal segments in liquid crystal shutters, they suffer from high capital costs and low material throughput, making them unsuitable for lowest cost high volume manufacturing.